This invention relates to radiation measuring apparatus and more particularly to apparatus for measuring a particular characteristic of a sample.
The present invention, while of general application, is particularly well suited for use in the quantitative analysis of blood or other body fluids. As is well known, for diagnostic purposes a plurality of samples of body fluid, flowing as serial segments in a stream spaced apart by bubbles of air or other inert fluid, commonly are individually and serially treated with one or more reagents to form a stream having an optical density at a particular wavelength which is indicative of a quantitative characteristic of the sample. In some cases, for example, the reagent comprises an acid solution having a distinct color which reacts with any glucose in the sample to produce a decrease in the density of the color proportional to the amount of glucose. The decrease in density is measured by a colorimeter, and the value is recorded in, say, milligrams of glucose per 100 milliliters of solution.
Heretofore, radiation measuring apparatus of the foregoing type exhibited certain disadvantages. As an illustration, in many such prior apparatus difficulties were encountered in cases in which a particular sample being analyzed exhibited high density and hence reduced the intensity of the radiation to be measured to a level below that at which accurate measurements could be obtained. Variations in the intensity of the radiation source for the apparatus also adversely affected the accuracy of the detected measurements. In addition, and this has been of special moment in cases in which the apparatus was arranged to provide direct readings of the concentration of a substance in the sample, it often was difficult heretofore to calibrate the response of the apparatus so that a given known standard solution resulted in a response at the proper position on the output scale.